The present disclosure is directed toward apparatus and methods for treating joints and in particular, to treating hip joints affected with osteoarthritis.
A joint is the location at which two or more bones make contact. Joints are constructed to allow movement and provide mechanical support, and are classified structurally and functionally. Structural classification is determined by how the bones connected to each other, while functional classification is determined by the degree of movement between the articulating bones. In practice, there is significant overlap between the two types of classifications.
There are three structural classifications of joints, namely fibrous or immovable joints, cartilaginous joints and synovial joints. Fibrous/Immovable bones are connected by dense connective tissue, consisting mainly of collagen. The fibrous joints are further divided into three types:                sutures which are found between bones of the skull;        syndesmosis which are found between long bones of the body; and        gomphosis which is a joint between the root of a tooth and the sockets in the maxilla or mandible.        
Cartilaginous bones are connected entirely by cartilage (also known as “synchondroses”). Cartilaginous joints allow more movement between bones than a fibrous joint but less than the highly mobile synovial joint. Cartilaginous joints include the artificial discs of the spine.
Synovial joints have a space between the articulating bones for synovial fluid. This classification contains joints that are the most mobile of the three, and includes the hip, knee and shoulder. These are further classified into ball and socket joints, condyloid joints, saddle joints, hinge joints, pivot joints, and gliding joints.
Joints can also be classified functionally, by the degree of mobility they allow. Synarthrosis joints permit little or no mobility. They can be categorized by how the two bones are joined together. That is, synchrondoses are joints where the two bones are connected by a piece of cartilage. Synostoses are where two bones that are initially separated eventually fuse together as a child approaches adulthood. By contrast, amphiarthrosis joints permit slight mobility. The two bone surfaces at the joint are both covered in hyaline cartilage and joined by strands of fibrocartilage. Most amphiarthrosis joints are cartilaginous.
Finally, diarthrosis joints permit a variety of movements (e.g. flexion, adduction, pronation). Only synovial joints are diarthrodial and they can be divided into six classes: 1. ball and socket—such as the shoulder or the hip and femur; 2. hinge—such as the elbow; 3. pivot—such as the radius and ulna; 4. condyloidal (or ellipsoidal)—such as the wrist between radius and carps, or knee; 5. saddle—such as the joint between carpal thumbs and metacarpals; and 6. gliding—such as between the carpals.
Synovial joints (or diarthrosis, or diarthroidal joints) are the most common and most moveable type of joints in the body. As with all other joints in the body, synovial joints achieve movement at the point of contact of the articulating bones. Structural and functional differences distinguish the synovial joints from the two other types of joints in the body, with the main structural difference being the existence of a cavity between the articulating bones and the occupation of a fluid in that cavity which aids movement. The whole of a diarthrosis is contained by a ligamentous sac, the joint capsule or articular capsule. The surfaces of the two bones at the joint are covered in cartilage. The thickness of the cartilage varies with each joint, and sometimes may be of uneven thickness. Articular cartilage is multi-layered. A thin superficial layer provides a smooth surface for the two bones to slide against each other. Of all the layers, it has the highest concentration of collagen and the lowest concentration of proteoglycans, making it very resistant to shear stresses. Deeper than that is an intermediate layer, which is mechanically designed to absorb shocks and distribute the load efficiently. The deepest layer is highly calcified, and anchors the articular cartilage to the bone. In joints where the two surfaces do not fit snugly together, a meniscus or multiple folds of fibro-cartilage within the joint correct the fit, ensuring stability and the optimal distribution of load forces. The synovium is a membrane that covers all the non-cartilaginous surfaces within the joint capsule. It secretes synovial fluid into the joint, which nourishes and lubricates the articular cartilage. The synovium is separated from the capsule by a layer of cellular tissue that contains blood vessels and nerves.
Various maladies can affect the joints, one of which is arthritis. Arthritis is a group of conditions where there is damage caused to the joints of the body. Arthritis is the leading cause of disability in people over the age of 65.
There are many forms of arthritis, each of which has a different cause. Rheumatoid arthritis and psoriatic arthritis are autoimmune diseases in which the body is attacking itself. Septic arthritis is caused by joint infection. Gouty arthritis is caused by deposition of uric acid crystals in the joint that results in subsequent inflammation. The most common form of arthritis, osteoarthritis is also known as degenerative joint disease and occurs following trauma to the joint, following an infection of the joint or simply as a result of aging.
Unfortunately, all arthritides feature pain. Patterns of pain differ among the arthritides and the location. Rheumatoid arthritis is generally worse in the morning; in the early stages, patients often do not have symptoms following their morning shower.
Osteoarthritis (OA, also known as degenerative arthritis or degenerative joint disease, and sometimes referred to as “arthrosis” or “osteoarthrosis” or in more colloquial terms “wear and tear”), is a condition in which low-grade inflammation results in pain in the joints, caused by wearing of the cartilage that covers and acts as a cushion inside joints. As the bone surfaces become less well protected by cartilage, the patient experiences pain upon weight bearing, including walking and standing. Due to decreased movement because of the pain, regional muscles may atrophy, and ligaments may become more lax. OA is the most common form of arthritis.
The main symptoms of osteoarthritis is chronic pain, causing loss of mobility and often stiffness. “Pain” is generally described as a sharp ache, or a burning sensation in the associated muscles and tendons. OA can cause a crackling noise (called “crepitus”) when the affected joint is moved or touched, and patients may experience muscle spasm and contractions in the tendons. Occasionally, the joints may also be filled with fluid. Humid weather increases the pain in many patients.
OA commonly affects the hand, feet, spine, and the large weight-bearing joints, such as the hips and knees, although in theory, any joint in the body can be affected. As OA progresses, the affected joints appear larger, are stiff and painful, and usually feel worse, the more they are used and loaded throughout the day, thus distinguishing it from rheumatoid arthritis. With progression in OA, cartilage looses its viscoelastic properties and it's ability to absorb load.
Generally speaking, the process of clinical detectable osteoarthritis is irreversible, and typical treatment consists of medication or other interventions that can reduce the pain of OA and thereby improve the function of the joint. According to an article entitled Surgical Approaches for Osteoarthritis by Klaus-Peter Günther, MD, over recent decades, a variety of surgical procedures have been developed with the aim of decreasing or eliminating pain and improving function in patients with advanced osteoarthritis (OA). The different approaches include preservation or restoration of articular surfaces, total joint replacement with artificial implants, and arthrodesis (fusion).
Arthrodesis are described as being reasonable alternatives for treating OA of small hand and foot joints as well as degenerative disorders of the spine, but were deemed to be rarely indicated in large weight-bearing joints such as the hip due to functional impairment of gait, cosmetic problems and further side-effects. Total joint replacement was characterized as an extremely effective treatment for severe joint disease. Moreover, recently developed joint-preserving treatment modalities were identified as having a potential to stimulate the formation of a new articular surface in the future. However, it was concluded that such techniques do not presently predictably restore a durable articular surface to an osteoarthritic joint. The correction of mechanical abnormalities by osteotomy and joint debridement are still considered as treatment options in many patients.
Joint replacement is one of the most common and successful operations in modern orthopaedic surgery. It consists of replacing painful, arthritic, worn or diseased parts of the joint with artificial surfaces shaped in such a way as to allow joint movement. Such procedures are a last resort treatment as they are highly invasive and require substantial periods of recovery. Joint replacement is sometimes called total joint replacement indicating that all joint surfaces are replaced. This contrasts with hemiarthroplasty (half arthroplasty) in which only one bone's joint surface is replaced and unincompartmental arthroplasty in which both surfaces of the knee, for example, are replaced but only on the inner or outer sides, not both. Thus, arthroplasty as a general term, is an operative procedure of orthopaedic surgery performed, in which the arthritic or dysfunctional joint surface is replaced with something better or by remodeling or realigning the joint by osteotomy or some other procedure. These procedures are also characterized by relatively long recovery times and are highly invasive procedures.
The currently available therapies are not condro-protective. Previously, a popular form of arthroplasty was interpositional arthroplasty with interposition of some other tissue like skin, muscle or tendon to keep inflammatory surfaces apart or excisional arthroplasty in which the joint surface and bone was removed leaving scar tissue to fill in the gap. Other forms of arthroplasty include resection(al) arthroplasty, resurfacing arthroplasty, mold arthroplasty, cup arthroplasty, silicone replacement arthroplasty, etc.
Osteotomy is a related arthroplasty procedure involving cutting of bone to improve alignment. The goal of osteotomy is to relieve pain by changing the anatomy and equalizing forces across the joint. This procedure is often used in younger, more active or heavier patients. Hip osteotomy involves removing bone from the femoral head or from the acetabulum of the hip joint and moving the bones slightly within the joint. This changes the position of the bones of the hip joint to shift the brunt of the patient's weight from damaged joint surfaces to healthier cartilage. A metal plate or pin is inserted to keep the bone in the new position.
Other approaches to treating osteoarthritis involve an analysis of loads which exist at a joint. Both cartilage and bone are living tissues that respond and adapt to the loads they experience. If a joint surface remains unloaded for appreciable periods of time the cartilage tends to soften and weaken. Further, as with most materials that experience structural loads, particularly cyclic structural loads, both bone and cartilage begin to show signs of failure at loads that are below their ultimate strength. However, cartilage and bone have some ability to repair themselves. There is also a level of load at which the skeleton will fail catastrophically. Accordingly, it has been concluded that the treatment of osteoarthritis and other conditions is severely hampered when a surgeon is not able to precisely control and prescribe the levels of joint load. Furthermore, bone healing research has shown that some mechanical stimulation can enhance the healing response and it is likely that the optimum regime for a cartilage/bone graft or construct will involve different levels of load over time, e.g. during a particular treatment schedule. Thus, there has been identified a need for devices which facilitate the control of load on a joint undergoing treatment or therapy, to thereby enable use of the joint within a healthy loading zone.
Certain other approaches to treating osteoarthritis contemplate external devices such as braces or fixators which control the motion of the bones at a joint or apply cross-loads at a joint to shift load from one side of the joint to the other. Various of these approaches have had some success in alleviating pain but suffer from lack of patient compliance or lack an ability to facilitate and support the natural motion and function of the diseased joint. Notably, the motion of bones forming a joint can be as distinctive as a finger print, and thus, each individual has his or her own unique set of problems to address. Some prior approaches to treating osteoarthritis have also been remiss in acknowledging all of the basic functions of the various structures of a joint in combination with its unique movement.
Osteoarthritis is the most common type of hip arthritis. As the protective cartilage is worn away by hip arthritis, bare bone is exposed within the joint.
Hip arthritis typically affects patients over 50 years of age. It is more common in people who are overweight, and weight loss tends to reduce the symptoms associated with hip arthritis. There is also a genetic predisposition of this condition, meaning hip arthritis tends to run in families. Other factors that can contribute to developing hip arthritis include traumatic injuries to the hip and fractures to the bone around the joint.
It has been reported that thirty-five percent of all osteoarthritis is found in the hips. In fact, it has been estimated that more than ten million American adults suffer from hip osteoarthritis and more than $6 billion is spent per year treating hip osteoarthritis. Hip osteoarthritis is particularly debilitating. Generally, it is believed that osteoarthritis of the hip is the most disabling of all joint osteoarthritis.
The most common symptoms of hip arthritis are pain with activities, limited range of motion, stiffness of the hip, walking with a limp, and decreased function, strength, activities and quality of life. Hip arthritis symptoms tend to progress as the condition worsens. Interestingly, hip arthritis symptoms do not always progress steadily with time. Often, patents report good months and bad months or symptom changes with weather accurately represent the overall progression of the condition.
Evaluation of a patient hip arthritis should begin with a physical examination and x-rays to determine which course of treatment should be followed. Weight loss is probably one of the most important, yet least commonly performed treatments. The less weight the joint has to carry, the less painful activities will be. Also, limiting certain activities may be necessary, and learning new exercise methods may be helpful. Strengthening of the muscles around the hip joint may help decrease the burden on the hip. Preventing atrophy of the muscles is an important part of maintaining functional use of the hip. Anti-inflammatory pain medications (NSAIDs) are prescription and nonprescription drugs that can help treat pain and inflammation. In more intrusive approaches, hip replacement surgery can hip resurfacing surgery have also been employed to treat hip osteoarthritis. In the most common hip replacement surgery, the cartilage is removed and a metal and plastic ball and socket hip replacement implant is placed in the hip. As an alternative to hip replacement, some patients are opting to pursue hip resurfacing surgery.
However, there is a need for a treatment modality which bridges the gap between the more conservative approaches such as weight loss, physical therapy and anti-inflammatory medicine and a decision to seek major surgical intervention. Such a treatment modality should be minimally invasive yet sufficiently effective to reduce the pain of osteoarthritis. The treatment should also be compatible with hip anatomy taking into consideration the many muscles overlaying the hip joint without hindering motion and avoiding the major arteries and nerves which are present.